1. Field of the Invention
The present invention relates to a variable lift valve operating system for an internal combustion engine comprising: an engine valve; a variable lift mechanism capable of changing a lift amount of the engine valve; and an actuator which is mounted on an engine body to rotatably drive a control shaft of the variable lift mechanism and which includes: an electric motor; a deceleration mechanism which decelerates output of the electric motor; a transmission mechanism interposed between the control shaft and the deceleration mechanism; and a default mechanism capable of rotatably biasing the control shaft to a position where a lift amount of the engine valve becomes a predetermined lift amount when the electric motor is not energized.
2. Description of the Related Art
Japanese Patent Application Laid-open No. 2005-42642 discloses an engine valve system, in which an actuator mounted on an engine body so as to drive a control shaft includes an electric motor, a screw shaft rotatably driven by the electric motor, and a nut that is connected to one end portion of a lever whose other end portion is fixed to the control shaft and that is threadedly fitted onto the screw shaft.
It is desirable that some of the components of the actuator of such a variable lift operating system be made of a synthetic resin for reduction in weight and friction, and that sensors whose characteristics change in accordance with the ambient temperature be mounted to the actuator, but the synthetic resin components and the sensors are vulnerable to heat. Meanwhile, since the actuator is mounted on the engine body, the actuator is exposed to rearward-blowing wind of a radiator or radiation heat from an exhaust system of the internal combustion engine depending on the mounting position of the actuator to the engine main body, so that the degree of freedom of the mounting position of the actuator using the thermally vulnerable parts is lowered.